Environmental Engineering Reference
In-Depth Information
6
Renewable Energy Generation in
Power Systems
6.1 Distributed Generation
6.1.1 Introduction [1 - 9]
Figure 3.2 in Chapter 3 shows that the maximum demand of England and Wales, a typical
developed European country, is of the order of 50 GW. Most of this power is supplied by
gas, coal and nuclear fuelled, combined cycle and steam driven generator sets rated up to
500 MW. The entire peak load, therefore, could be met by a hundred or so sets. As most
power stations have two, three, or four such generator sets only a few tens of power stations
are required to supply the many millions of consumers that are connected to the system. This
type of generation is known as centralized generation and is typical of large power systems
worldwide. Centralized generation is normally connected to the transmission system.
The term distributed generation or embedded generation refers to smaller generators that
are usually connected to the distribution network. Distributed generation includes:
￿ generators powered from renewable energy sources (except large scale hydro and the
largest wind farms);
￿ combined heat and power (CHP) systems, also known a co-generation (co-gen);
￿ standby generators operating grid connected, particularly when centralized generation is
inadequate or expensive.
The focus here is on renewables, but much of this chapter applies equally to all three types
of distributed generation.
Smaller generators are not connected to the transmission system because of the cost of
high voltage transformers and switchgear. Also, the transmission system is likely to be too
far away since the geographical location of the generator is usually predetermined by the
availability of the renewable energy resource. Such generators are embedded in the distribu-
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